This week I encountered at least two links in the forum that didn't work (404), both because the link included an extra character at the end (comma or dot). When I remove the extra char it works. I know I saw this in the past, but very infrequently, so I think this could be also caused by some recent change in the forum settings / version / JavaScript library of the editor...
Update: it looks like the problem might be only when clicking a link from an email, see my 1st reply